This invention relates to on-line monitoring of performance losses due to reduced conductivity of a heat exchanger resulting from fouling of the surfaces of the heat exchanger. Monitoring the effect of scaling and micro-bio fouling, both contributing to fouling occurring within operating heat exchangers and condensers is often difficult since conventional measured operating parameters can not easily isolate fouling effects from other monitored performance losses. Typically prior art monitors of performance losses of heat exchangers have used indirect measurements, such as inlet header temperature compared with discharge header temperature, vacuum in the condenser section and aggregate flow measurements for calculating an estimated fouling factor for an operating heat exchanger, wherein the calculated performance results were actually estimates as they lacked accuracy.
It is for this reason, prior efforts have recently been directed toward development of side-stream monitoring units which attempt to simulate operating conditions of an operating exchanger. If working parameters such as heat flux, fluid flow and tube metallurgy can be duplicated, it is assumed that fouling will, likewise, be similar. Applicant is aware of one such prior art device covered by U.S. Pat. No. 4,762,168 to Kawabe et al. which includes a by-pass line having a monitor tube of the same material and size as the condenser tubes. Although such prior art side-stream units appear promising, especially for the simultaneous testing of various fouling control options, they cannot replicate all conditions of a full-scale condenser or exchanger, for example tube length, temperature rise, tube aged condition, changing load and flow parameters, etc. For this reason, side-stream monitoring systems are often viewed with skepticism by plant performance engineers when they are used as monitors for condensers or heat exchangers.
Applicant is aware of additional prior art attempts at on-line monitoring which have been met with varying degrees of success, in particular a device disclosed by ESEERCO in 1987.
ESEERCO investigated using an instrumented probe which is inserted trough the discharge water box of a condenser and traverses the free jet of cooling fluid characteristically emanating from individual heat transfer tubes. The probe instrumentation includes fluid temperature and flow (pitot) sensors, which provides discharge fluid temperature and flow velocity data for each traversed tube. This information is combined with the inlet water temperature, and the saturated steam temperature calculated from steam back pressure data. These data are then used to calculate heat transfer resistances for individual heat transfer tubes. The major disadvantages of the ESEERCO approach are:
1. Perfect alignment of the probe with each measured heat transfer tube is critical since a slight offset will significantly influence flow measurements of the probe. PA1 2. Steam temperature for the heat transfer tube being monitored is not measured , but is assumed to be the same as the average condenser temperature--this assumption may not be correct. PA1 3. The approach does not lend itself easily to continuous on-line monitoring. PA1 1. During the measuring process, the water temperature is raised to the steam saturation temperature, which is often high enough to destroy biofilm attached to the heat transfer tubes with the result that harmful scaling could result. PA1 2. The rapid hydraulic closing and reopening of selected tubes creates a flow excursion which has been shown to result in significant sloughing of attached fouling deposits. PA1 V=Coolant Flow Rate (M/sec) Each Tube PA1 Q.sub.H =Heat Flux (watts) PA1 T.sub.I =Coolant Inlet Temperature (.degree.C.) PA1 T.sub.E =Coolant Outlet Temperature (.degree.C.) PA1 T.sub.S =Steam Temperature (.degree.C.) PA1 U=Heat Transfer Coefficient (watts/M.sup.2 -.degree.C.) PA1 R.sub.T =Heat Transfer Resistance (M.sup.2 -.degree.C./watts) PA1 LMTD=Logarithmic Mean Temperature Difference PA1 A.sub.H =Area, Heat Exchanger (Effective) (M.sup.2) PA1 A.sub.C =Area, Tube Cross Section (M.sup.2) PA1 C.sub.P =Specific Heat of Water (watts/.degree.C.-Kg) PA1 P=Density of Water (Kg/M.sup.3) PA1 M=Mass Flow of Coolant Water (Kg/sec) ##EQU1## reorganizing yields: solving for 1/U=R.sub.T by definition ##EQU2##
Czolkoss (Taprogge Inc.) as disclosed in 1990 uses another approach to on-line monitoring connected directly to an operating heat exchanger . The Czolkoss method uses miniature thermocouples mounted on the inlet and outlet of each heat transfer tube to be monitored,as is shown in FIG. 9, a hydraulic closure device is mounted on the discharge tube sheet and serves to close a selected tube for some time. Over a ten minute period, the coolant water in the tube assumes the temperature of steam being condensed in the condenser and therefore determines the steam temperature. The tube is then reopened. In the Czolkoss method the outlet thermocouple first measures the saturated steam temperature, then after a certain period of time (T.sub.0), measures the discharge water temperature. The amount of time required to go from the steam temperature to the discharge temperature is directly correlated to the flow velocity of coolant water. With this data, the on-line heat transfer coefficient is then calculated.
This method overcomes many of the disadvantages of the transverse probe of ESEERCO, but has several major drawbacks of its own, including:
The problem not recognized by the prior art is that performance sensors fail to provide accuracy in directly measuring temperature and flow parameters in a heat exchanger while operating, because they interfere with the operation of the system as installed, with the result that the parameters to be tested are altered. Heretofore such interference has been compensated for by values not directly measured, but computed, or given an assumed value.
The ideal condition for monitoring fouling within condenser or exchanger systems requires a method to accurately measure change in heat transfer of the system as measured by change in heat transfer of actual heat transfer tubes within the heat exchanger while the heat exchanger is operational, or, in other words, an on-line fouling monitor.
The present invention has solved this problem in a novel fashion by providing internal temperature and internal flow sensors positioned in individual heat transfer tubes connected by circuitry with a monitor. This system provides for continuous on-line measurement of temperature and flow values in an operational heat exchanger with continuous measurement, calculation and display of performance characteristics, without altering the operating characteristics or environment of the system being monitored. In so doing, it is found desirable to provide a new and improved on-line monitoring device and method whereby said the on-line monitoring device provides accurate measurement of the combination of measurement of reduced conductivity of a heat exchanger resulting from scaling or micro-bio fouling and a cooling water flow sensor wherein the on line monitor continually monitors the signals of the temperature and flow sensor to provide a continuous reading of the heat transfer co-efficient determining any deterioration in the performance of the heat exchanger and to overcome at least some of the disadvantages of the prior art heat exchanger performance devices and methods.